How Is Thymus Cancer Diagnosed?

If there is a reason to think you might have a tumor of the thymus, your doctor will ask you about symptoms and use one or more exams or tests to find out if the disease is really present. Certain signs and symptoms might suggest that a person may have a thymus tumor, but tests are needed to confirm the diagnosis.

Medical history and physical exam

If you have signs or symptoms that suggest you might have a thymus tumor, your doctor will want to take a complete medical history to check for symptoms. You will also be asked about your general health.

A physical exam provides information about possible signs of thymic cancer and other health problems. Patients with thymic cancer will sometimes have a fullness that the doctor can feel in the lower neck area.

Thymomas are often suspected because the patient has signs and symptoms associated with myasthenia gravis, hypogammaglobulinemia, or red cell aplasia.

If symptoms and/or the results of the physical exam suggest a thymus tumor might be present, more tests probably will be done. These might include imaging tests, lab tests, and other procedures.

Imaging tests

Imaging tests use x-rays, magnetic fields, or radioactive substances to create pictures of the inside of your body. Imaging tests may be done for a number of reasons, including to help find a suspicious area that might be cancerous, to learn how far cancer may have spread, and to help determine if treatment has been effective.

Chest x-ray

A chest x-ray may be the first imaging test a doctor orders if he or she suspects a problem in the middle of the chest. It may be able to show if there is a tumor in the chest. In some cases, a chest x-ray may find tumors in people before they cause any symptoms (when the person is having the x-ray done for another reason). However, some thymomas are small or are in certain places that may not show up on a chest x-ray. If your doctor is still suspicious or if an abnormality appears on the chest x-ray, a CT scan may be ordered.

Computed tomography (CT) scan

The computed tomography (CT) scan is an x-ray procedure that produces detailed cross-sectional images of your body. Instead of taking one picture, like a regular x-ray, a CT scanner takes many pictures as it rotates around you while you are lying on a narrow platform. A computer then combines these into images of slices of the part of your body that is being studied.

Before the test, you may be asked to drink 1 to 2 pints of a liquid called oral contrast. This helps outline abnormal areas in the body. You may also receive an IV line through which a different kind of contrast dye (IV contrast) is injected. This helps better outline structures such as blood vessels in your body.

The injection can cause some flushing (redness and warm feeling that may last hours to days). A few people are allergic to the dye and get hives. Rarely, more serious reactions like trouble breathing and low blood pressure can occur. Medicine can be given to prevent and treat allergic reactions. Be sure to tell the doctor if you have ever had a reaction to any contrast material used for x-rays.

A CT scanner has been described as a large donut, with a narrow table in the middle opening. You will need to lie still on the table while the scan is being done. CT scans take longer than regular x-rays, and you might feel a bit confined by the ring while the pictures are being taken.

CT scans can have several uses:

  • CT scans of the chest can spot very small tumors and help determine the exact location and extent of the tumors.
  • CT scans can be helpful in staging a cancer (determining the extent of its spread). For example, they can show whether the cancer has spread to nearby lymph nodes or to the liver, kidneys, brain, or other organs.
  • CT scans can also be used to guide a biopsy needle precisely into a suspected tumor or metastasis. For this procedure, called a CT-guided needle biopsy, the patient remains on the CT scanning table while a radiologist advances a biopsy needle through the skin and toward the location of the mass. CT scans are repeated until the needle is within the mass. A biopsy sample is then removed and looked at under a microscope.
  • During or after treatment, CT scans may be used to see whether tumors are shrinking or have recurred (come back) in other parts of the body.

Magnetic resonance imaging (MRI) scan

Like CT scans, MRI scans provide detailed images of soft tissues in the body. But MRI scans use radio waves and strong magnets instead of x-rays. The energy from the radio waves is absorbed and then released in a pattern formed by the type of body tissue and by certain diseases. A computer translates the pattern into very detailed images of parts of the body. A contrast material called gadolinium is often injected into a vein before the scan to better see details.

MRI scans may be a little more uncomfortable than CT scans. They take longer — often up to an hour. You may be placed inside a large cylindrical tube, which is confining and can upset people with a fear of enclosed spaces (claustrophobia). For people who cannot tolerate a regular MRI machine, there are special, more open MRI machines that can be used instead in some cases. The MRI machine makes buzzing and clicking noises that you might find disturbing. Some places will provide earplugs to help block this out.

MRI of the chest may be done to look more closely at thymus tumors. They are most often used when the patient can’t have a CT scan for medical reasons (like problems with the IV contrast). MRI images are also particularly useful in looking for cancer that may have spread to the brain or spinal cord.

Positron emission tomography (PET) scan

For a PET scan, you receive an injection of a substance that contains a radioactive atom. This is usually glucose (a type of sugar), but other substances that are attracted to thymoma cells may also be used. The amount of radioactivity is very low. The cancer cells in the body absorb large amounts of the radioactive substance. A special camera can then be used to create a picture of areas of radioactivity in the body. The picture is not finely detailed like a CT or MRI scan, but it can provide helpful information about your whole body.

A PET scan can help give the doctor a better idea of whether an abnormal area seen on another imaging test is a tumor or not. If you have already been diagnosed with cancer, your doctor may use this test to see if the cancer has spread to lymph nodes or other parts of the body. A PET scan can also be useful if your doctor thinks the cancer may have spread but doesn’t know where.

Certain machines are able to perform both a PET and CT scan at the same time (PET/CT scan). This lets the doctor compare areas of higher radioactivity on the PET scan with the more detailed appearance of that area on the CT. Combined PET/CT is used more often than PET (alone) in looking at thymomas.

Blood tests

Blood tests can’t be used to diagnose thymomas directly, but they may still be helpful in some situations. For example, tests may be done to look for certain antibodies in the blood of people who may have myasthenia gravis or other autoimmune disorders. Other blood tests may be done to make sure a mass in the middle of the chest isn’t a germ cell tumor or part of the thyroid gland.

If a thymoma is diagnosed, blood cell counts and blood chemistry tests are done to get an idea of a person’s overall health, especially if surgery is planned. Also, tests for myasthenia gravis (MG) will be done before any surgery. This is because MG is very common in patients with a thymoma, and, if left untreated, it can cause problems with anesthesia during surgery. People getting chemotherapy also have regular blood tests to make sure the drugs aren’t having unwanted effects on the bone marrow, kidneys, or other organs.

Types of biopsy procedures

Although signs, symptoms, and imaging tests can suggest that a thymic tumor is likely to be present, doctors can’t be certain of the diagnosis without looking at the tumor under a microscope.

For most cancers, removal of a small sample of the tumor (known as a biopsy) is needed to confirm whether a tumor is present and, if so, to determine its type. For thymomas, this is rarely done because doctors can usually tell that the tumor is very likely a thymoma based on how it looks on imaging tests. Because of this, doctors often remove the entire tumor rather than do a biopsy. If the doctor suspects a different type of tumor, a biopsy may be done before surgery. Most often, a needle biopsy is done. A biopsy may also be done to confirm the diagnosis if the tumor can’t be removed completely with surgery. This can allow the cancer to be treated with things other than surgery.

Needle biopsy

Tumors in the chest are sometimes sampled by needle biopsy. A long, hollow needle is passed through the skin in the chest. Imaging tests such as CT scans are used to guide the needle into the tumor so that a small sample can be removed to be looked at under the microscope. This procedure is done without a surgical incision or overnight hospital stay.

A possible downside of this test is that it might not always get enough of a sample to make an accurate diagnosis or allow the doctor to get a good sense of the extent of the tumor.

Surgical biopsy

In most cases, if the doctor believes that the patient has thymoma (based on CT findings and lab tests, especially in a patient with a paraneoplastic syndrome) and it can be removed with surgery, the doctor may operate without any biopsy. This can both provide enough of a sample for a diagnosis and treat the tumor at the same time. The specimen is sent to the lab after surgery to confirm the diagnosis. See Surgery For Thymus Cancer for more information.

The American Cancer Society medical and editorial content team
Our team is made up of doctors and master’s-prepared nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

Last Medical Review: February 7, 2014 Last Revised: March 17, 2015

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